<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        h3{
            /*正常粗细*/
            font-weight: 400;
        }
        div{
            /*加粗*/
            font-weight: 700;
        }
    </style>
</head>
<body>
    <h3>h3</h3>
    <div>div标签</div>
</body>
</html>